It is known to mine by excavation using a screw type excavator which can cut arcuate or cylindrical cross-sectional excavations into the material to be mined, e.g. coal. In a known device, according to German Pat. No. 1,283,177, screw sections of a screw type excavator are all moved together with corresponding trough sections in a rigid fashion, e.g. ramlike fashion, against the wall of coal forming the face of a seam for excavation mining.
The device moves as a unit in an uninterrupted front, orthogonally towards and into the wall or face of coal so that the entire length of the screw assembly must be effective to bite into the face. Accordingly, a high torque must be transmitted to the screw shaft and the overall power requirements for mining of coal according to this method are high.
Where very long coal walls are to be mined, screw excavating and conveying apparatus of the prior art type cannot be economically employed because of the high power requirements. These problems are also not completely overcome when the excavator is advanced with the aid of a special skid mounting or sled device, as a unit to and fro and additionally parallel along the wall of the body of coal, since any savings in torque transmitted to the screw shaft is offset by additional power consumed in the back-and-forth movement of the screw of the screw excavator.
In general, the screw is employed for excavating of material to be mined and for the conveying of the excavated or mined material aong a longitudinal axis, parallel to the screw shaft, to a suitable collection point.